1. Field of the Invention
The present invention relates to an image sensor and more particularly, to an image sensor using a solid state image sensing device.
2. Description of the Prior Art
In case that a solid state image sensing element such as CCD (Charge-Coupled Device) is used in a television camera, it has been proposed to make the storage time of the image sensing element shorter than the field (or frame) time of the television signal by changing a drive method of the solid state image sensing element. For instance, assuming that a substantial storage time t1 is 1/500 sec, the ratio of the storage time t1 during which the charges to be excluded are accumulated, to tl becomes; EQU t2/t1=(1/60=1/500)/1/500=7.3
which indicates that t2 is about 7.3 times as long as t1. If the charges accumulated during t1 are assumed as a standard level, charged about 7.3 times as much as the standard level are accumulated during t2. If a great amount of charges are accumulated, it is very difficult to exclude all of the charges from the image sensing element without affecting the substantial storage time. Particularly, since for example a highlight part on the screen generates a large amount of charges, a vertical transfer for charge exclusion during the vertical period may cause a large amount of residual charges, thereby resulting in an adverse effect upon an output image.